Method for drilling with improved fluid collection pattern

ABSTRACT

A method for improving underground fluid collection and removal. The method includes drilling one well with a vertical section and a horizontal section having main bores and branches. All of the branches are substantially in one horizontal plane except one branch for each main bore. That one branch for each main bore is slope downward towards a common place, where a second vertical well is drilled for collecting fluid. A system resulting from the method is also claimed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of a U.S. provisional patentapplication, Ser. No. 60/476,964, filed on Jun. 9, 2003, with the sametitle, by the same inventor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to underground fluid (liquid and/or gas)collection and production, particularly to coal seam methane gasproduction and water drainage, and to an improved drainage pattern forgas and liquid collection.

2. Description of the Related Art

Subterranean deposits of coal may contain substantial quantities ofentrained fluid, such as methane gas, oil and water. The entrained gasand liquid can be safety hazards for coal mining, especially the methanegas. The removal of entrained gas and liquid can make the coal miningsafer and more productive. Although methane gas poses safety concerns incoal mining operations, it is actually one of the cleanest fuelsavailable. Its demand has been increasing steadily. In recent years,methane gas removed from coal deposits has become a useful product in itown right or even a main product. Substantial obstacles, however, havefrustrated more extensive development and use of methane gas deposits incoal seams. The foremost problem in producing methane gas from coalseams is that while coal seams may extend over large areas of up toseveral thousand acres, the coal seams are fairly thin, varying from afew inches to several meters. Thus, while the coal seams are oftenrelatively near the surface, vertical wells drilled into the coaldeposits for obtaining methane gas can only drain a fairly small radiusaround the coal deposits. Further, coal deposits are not amendable topressure fracturing and other methods often used for increasing methanegas production from rock formations. As a result, once the gas easilydrained from a vertical well bore in a coal seam is produced furtherproduction is limited.

Additionally, coal seams are often associated with subterranean water,which must be drained from the coal seam at the time the methane ismined. The separation of gas (mostly methane) and liquid (mostly water)is necessary for efficient production or removal of either one.

Horizontal drilling patterns have been tried in order to extend theamount of coal seams exposed to a drill bore for gas extraction. A roottype or a pinnate type pattern is generally used. A vertical welllocated at the center of the pattern, with main bores/branches radiatingoutwards. Each main bore may in turn have branches to fill the space inbetween the main bores.

Gases in coal seam may be produced or removed prior to coal miningoperation. Vertical well and horizontal bores are drilled. Many of theexisting drilling patterns require drilling of several vertical wells incooperation with horizontal bores in addition of main vertical well.Many of the patterns in the art are not flexible enough to be useful forvarious field conditions.

It is desirable to have a method and a system to improve the drainagepattern such that the number of vertical wells for a particular field isreduced and the drainage from such field is improved.

BRIEF SUMMARY OF THE INVENTION

The present invention uses a primary well and a secondary well. Theprimary well has a vertical section and substantially horizontalsection. The horizontal section forms a root pattern, with main boresand side branches. From each main bore, there is one side branch thatwill convene at a common location. The common location where the sidebranches convene is deeper than all other main bores or their sidebranches, which are substantially horizontal. At the common location, asecondary vertical well is drilled. Liquid and gas from all brancheswill flow to the common location by gravity and/or pressure andthereafter removed through the secondary vertical well.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A better understanding of the invention can be had when the followingdetailed description of the preferred embodiments is considered inconjunction with the following drawings, in which:

FIG. 1 a perspective view depicting the overall drainage system with aprimary well, a secondary well and a horizontal drainage branches.

FIG. 2 is an elevation view depicting the relative elevation of primarywell and the secondary well with connecting branches.

FIG. 3 is a plane view depicting the horizontal projection and theinterconnection of horizontal well bore branches.

FIG. 4 is an elevation view depicting the primary well and one of themain horizontal main bores.

FIG. 5 depicts the details around the intersection of secondary well andthe convening branches without direction connections between thesecondary well and the convening branches.

FIG. 6 depicts an alternative to the system in FIG. 5, where thebranches are directly connected to the secondary well.

FIG. 7 is a plane view depicting the horizontal projection of analternative system.

FIGS. 8-10 depict an alternative system where horizontal branches bypassthe vicinity of the secondary well.

FIGS. 11-15 depict alternative fluid collection systems.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 depicts an overall system 15 for underground fluid collection,and production/removal. As used in coal seam gas production or coalmining degasification, a primary well 20 and a secondary well 30 may bedrilled In certain coal fields, the vertical sections of one or bothwells may be existing wells. The primary well 20 has a vertical section22 and a substantially horizontal section 24. The primary well 20 isused primarily for fluid collection. The horizontal section 24 is afluid communication and transportation network, similar to a root systemfor a tree or the veins in a tree leaf. The horizontal section hasseveral main bores 40, 50, 60 etc. Each main bore has a plurality ofbranches to get into a larger area to increase the contact surface areasbetween the horizontal section and the fluid bearing formation. Thefluid entrained in the surrounding area in the coal seam or otherformation will migrate into the branches, due to the gas partialpressure difference and/or gravity. Once the fluid gets into thehorizontal branches, its mobility is enhanced greatly and will freelymove to a location where the partial pressure is lower or the elevationis lower. As to coal seam gas production, the gas bearing formation isthe coal seam, which is often relatively thin, ranging from less than afoot to tens of feet. The horizontal section of well bores issubstantially confined in that coal seam. The elevation of thehorizontal section depends largely on the elevation of the coal seamformation which is substantially flat or varying gradually in a typicalcoal field.

Referring now to FIG. 2, from a main bore or a branch, a C-branch may bedrilled. A C-branch is same as any other braches and may be drilled bythe same drilling rig. The only difference is that a C-branch is notsubstantially horizontal. A C-branch is typically inclined. A C-branchwill start from a main bore or a branch and terminate at a vicinity ofcommon location. A C-branch may or may not be confined within the coalseam. Typically, a C-branch is not confined within the coal seam, whereother main bores or horizontal branches are typically confined in thecoal seam. The elevation of the beginning of the C-branch is the same asthe most parts of the horizontal section, but the elevation of theending of the C-branch is typically lower than the rest of thehorizontal section, such that the fluid in main bores or branches tendsto flow towards the ending of the C-branch. Once the horizontal sectionwith transportation network is formed and the common location isdetermined, a secondary well 30 is drilled at the common location or anexisting vertical well at the common location is utilized. The bottom ofthe secondary well 30 is at or slightly below the ends of the C-brancheswhich convene there. The ends of C-branches may intersect the secondarywell as in the alternative may merely terminate in the vicinity of thesecondary well. In typical drilling operations and typical undergroundformation of the C-branch terminates in the vicinity of a drilled well,the well bore is likely fractured, i.e. permeable to fluid. Therefore,it is often unnecessary for the ends of C-branches to intersect with thesecondary well. There will be sufficient communication between theC-branches and the secondary well 30 for fluid to freely move betweenC-branches, the horizontal section 24 of primary well 20 and thesecondary well 30. The permeable formation surrounding the secondarywell 30 may act as a filter to screen out debris from reaching thesecondary well 30 and the pumping devices.

FIG. 2 depicts more details regarding the elevation relationship betweenthe primary well 20, secondary well 30 and horizontal main bore 40 andC-branch 140. Related FIGS. 5 and 6 depict the common location whereends of C-branches and bottom of secondary well 30 convene. Typically,the vertical section 22 of the primary well 20 curves above the coalseam and turns into horizontal main bore 40. The C-branch 140 starts outfrom main bore 40, which is at the same elevation as most other parts ofthe horizontal section, ends at the common location, at a lowerelevation. The bottom of the secondary well 30 is at the same vicinity.All the C-branches and the secondary well 30 may be interconnected toeach other at the common location as shown in FIG. 6. C-branch 140 andC-branch 150 are connected to the secondary well 30 at a similarelevation. Fluids collected by the horizontal well bores are transportedby C-branches to the bottom of secondary well 30 and may thereafter beremoved. Alternatively, the C-branches may simply end at a vicinity ofthe common location as shown in FIG. 5, without actually interconnectingwith each other. As shown in FIG. 5, after drilling of C-branches, e.g.140, secondary well 30, the vicinity at common location 1000 that mayhave been fractured and permeable to fluid. These fractures may happenduring the drilling of either the secondary well 30 or the C-branches orother branches nearby. The fluid in any of the well bores cancommunicate and flow to the secondary well 30 easily and freely.Beneficially, the fractured formation 1000 serves to block debris in onewell bore from traveling to another or to the secondary well 30. If asump pump is situated at the bottom of secondary well 30 for removingsubterranean water, then debris from all horizontal section of theprimary well 20 will be blocked by the filter effect of the fracturedformation. The distance between the secondary well 30 and the C-branchends may be as close as a few inches, e.g. one inch or as large as tensof feet, e.g. 90 feet depending on the permeability of the materialbetween the terminus of C-branch 140 and secondary well 30. Thediameters of the wells and well bores are in the range of several inchesto a few feet. Typical well bores are 6 to 10 inches in coal seammethane production.

FIG. 3 depicts a horizontal projection of the horizontal section of theprimary well 20. The vertical section 20 is at the center of the wholesystem. The main bores, e.g. 40, 50 and etc., radiate outwards to theboundaries of the coal field so as to cover the whole coal field. Eachmain bore has a plurality of branches, e.g. 240, 250 etc., to providebetter coverage in between the main bores. Several C-branches convene atthe vicinity of the secondary well 30.

FIG. 4 depicts the elevational relationships of the various sections ofthe primary well 20. The vertical section 20 is substantially straightand vertical. It curves near the target coal seam and becomes ahorizontal section, a main bore 40. The main bore 40 extends outwardswithin the coal seam, substantially in the same elevation. A branch 240,which is substantially at the same depth, is shown in FIG. 4.

FIG. 7 depicts an alternative embodiment of the current invention.Instead of sharing a common vertical section of the primary well withdifferent horizontal main bores, in this alternative, each main bore 20and 21 has its own vertical well not show in FIG. 7. In thisarrangement, the vertical wells and the horizontal main bores can bedrilled simultaneously and independently. The C-branches still conveneat a common location and a common secondary well 30 is drilled tocollect the liquid or gas.

FIGS. 8, 9 and 10 further illustrate the liquid collection system wherethe secondary well 1030 is not directly connected to the branches ormain bores of the primary well 1020. FIG. 8 is a horizontal projectionof the system, where primary well 1020 has a horizontal section withmain bores and branches, e.g. 1140 and 1150. The secondary well 1030 islocated at the vicinity of branches 1140 and 1150 but not directlyconnected to either of the branches. Due to the drilling operation ofthe secondary well 1030, branches 1140 or 1150, or their combination,the underground area in the vicinity of braches 1140 and 1150 arefractured, or generally permeable to fluids. Therefore any fluid inbranches 1140 and 1150 may flow into the secondary well 1030. FIGS. 9and 10 show the vertical cross-section along the line A-A′ and B-B′,illustrate the vertical or elevation relationship between the secondarywell and the branches. As shown in FIG. 9, the primary well 1020 has avertical section, a curve and then a horizontal section. The horizontalmain bore branch extends from the primary well 1020 towards thesecondary well 1030. The main bore then bends and through the vicinityof the secondary well 1030. FIG. 10 shows the branches 1140 and 1150pass the vicinity secondary well 1030. The two branches 1040 and 1050have a higher elevation than the bottom of the secondary well 1030.

FIGS. 11-16 depict alternative systems for fluid collection. FIGS. 11and 12 show the vertical projection and horizontal projection of asystem. The secondary well 2030 is at or near a minimum elevation of acoal bed. The primary well 2020 is at a higher elevation of the coalbed, such that the horizontal section of the primary well 2020 bypassesthe secondary well 2030. The fluid collected by the horizontal sectionof primary well 2020 will flow towards the low point at secondary well2030.

FIGS. 13 and 14 depict another alternative system, where the coal bedgoes slightly down hill from the primary well 3020 to the secondary well3030. FIG. 13 shows the horizontal projection and the FIG. 14 shows thevertical projection. The horizontal branch 3040 goes slightly downwardfrom primary well 3020 to secondary well 3030 and the C-branch 3140further the vicinity of secondary well 3030.

FIG. 15 depicts approaches the horizontal projection of an alternativesystem. The horizontal branches from the primary well 4020 splits nearthe secondary well 4030 and bypasses the secondary well 4030.

The locations of the primary well and the secondary well may beindependent from each other. They can be very close to each other, e.g.300 ft or far away, e.g. 2000 ft or 4000 ft, at the opposite end of acoal field. Relative locations are determined to form a best gascollection/liquid drainage pattern. If there are existing vertical wellsin a coal field, then those wells may used as the primary or secondarywells and be modified to suit the new needs. The flexibility of thelocation of the primary and secondary wells make the current fluidcollection pattern more efficient and more economical than existingfluid collection methods. For example, in a coal field where the coalbed is sloped towards one side, then the secondary well may be locatedat the lowest edge of the coal seam while the primary well may belocated at the highest edge of the coal seam, such that water can draintowards the secondary well. Water collected may thereafter be pumped outof the coal seam.

If the coal seam has both an uphill and a downhill slope, then thesecondary well may be located at the valley of the coal seam, forexample as shown in FIGS. 11 and 12.

C-branch is used primarily to transport the fluid collected from thecoal seam in the main bores and branches in the horizontal well bore.C-branch has a different functionality compared to other main bores andbranches, which are used for collecting fluid from coal seam. Therefore,C-branches are not confined within the coal seam. Therefore, C-branchesmay be sloped from the substantially horizontal well bores of main boresand branches towards a lower elevation at the secondary well, to serveas a sink for fluid, where the collected fluid may thereafter be removedfrom the site. C-branch sloping patterns provide and make the fluidcollection and removal more efficient and effective.

Unlike prior art drainage patterns, where each main bore has a verticalwell for liquid collection and removal, according to the currentinvention, the secondary well may be shared among two or more mainbores. Thus the number of vertical wells is reduced.

In some large fields as shown in FIG. 3, the primary well 20 is at thecenter of the field, or the main bores radiate outwards to the edge ofthe field.

While illustrative embodiments of the invention have been depicted anddescribed, it will be appreciated that various modifications andimprovements may be made without departing from the spirit and scope ofthe invention.

1. A method for collecting and removing fluid from underground deposits,the method comprising: drilling a first, substantially vertical well;drilling a substantially horizontally well with at least one main borefrom the first substantially vertical well; drilling a plurality ofbranches in the horizontal plane from a main bore; drilling a second,substantially vertical well deeper than all the main bores and branchesof the horizontal well; and drilling a C-branch from a main bore towardsthe second well.
 2. The method in claim 1, wherein the C-branchintersects the second well.
 3. The method in claim 1, wherein theC-branch bypasses the second well at a minimum distance d.
 4. The methodin claim 1, wherein the C-branch terminates at a distance d from thesecond well.
 5. The method in claim 3, wherein the minimum distance dranges 1 inch to 100 feet.
 6. The method in claim 5, wherein the fluidcollected at the second well is water or gas.
 7. The method in claim 1,further comprising: removing fluid from the second well.
 8. The methodin claim 1, wherein the distance between the first well and the secondwell ranges from 300 feet to 4000 feet.
 9. A method for collecting andremoving fluid from underground fluid deposits, the method comprising:drilling a first, substantially vertical well; drilling a substantiallyhorizontal well with at least one main bore from the first substantiallyvertical well; drilling a plurality of branches in the substantiallyhorizontal plane from the said main bore; drilling a second,substantially vertical well at the vicinity of the main bore or abranch, wherein the minimum distance between the second well, and thebranch or the main bore is d, wherein the bottom of the second well isdeeper than all the main bores and branches.
 10. The method in claim 9,wherein the minimum distance d ranges from 1 inch to 100 feet.
 11. Themethod in claim 9, wherein the horizontal distance between the secondwell and the vertical section of the first well ranges from 300 feet to4000 feet.
 12. The method in claim 9, further comprising: fracturing thestrada between the second well, and the branch or the main bore.
 13. Awell system for underground fluid collection and removal, the systemcomprising: a first well having a substantially vertical section and asubstantially horizontal section; wherein the substantially horizontalsection comprises at least one main bore and a plurality of branches;wherein the main bore further has a C-branch; a second well having asubstantially vertical section wherein the bottom of the second well islower than any main bores or branches; wherein the C-branch inclinesdownward towards the second well and terminates at the vicinity of thesecond well.
 14. The well system in claim 13, wherein the C-branchconnects to the second well.
 15. The well system in claim 13, whereinthe minimum distance d between the C-branch and the second well isgreater than zero.
 16. The well system in claim 15, wherein the minimumdistance d ranges from 1 inch to 100 feet.
 17. The well system in claim13, wherein the first well and the second well are in a coal field, andwherein substantially all main bores and branches of the horizontalsection are in a coal seam except the C-branch.
 18. The well system inclaim 13, further comprising: a third well having a substantiallyvertical section and a substantially horizontal section; wherein thesubstantially horizontal section comprising at least one main bore and aplurality of branches; wherein the main bore further has a secondC-branch; wherein the second C-branch inclines downward towards thesecond well and terminates at the vicinity of the second well.
 19. Thewell system in claim 18, wherein the first well, the second well and thethird well are in a coal field, and wherein substantially all main boresand branches of the horizontal section are in a coal seam except theC-branch and the second C-branch.
 20. The well in claim 18, wherein thehorizontal distance between the vertical section of the third well andthe second well ranges from 300 ft to 4000 ft.
 21. The well in claim 13,wherein the horizontal distance between the vertical section of thefirst well and the second well ranges from 300 ft to 4000 ft.